Underground storage



Feb. 14, 1961 J. H. ALLEN UNDERGROUND STORAGE 2 Sheets-Sheet 1 Filed May 29, 1,95 v

INVENTOR. J H ALLEN llll l lli A T TORNEVS FIG.

Feb. 14, 1961 J. H. ALLEN 50 UNDERGROUND STORAGE Filed May 29, 1958 2 Sheets-Sheet 2 INVENTOR. J.H. ALLEN A TTORNEVS United States Patent UNDERGROUND STORAGE James H. Allen, New York, N.Y., assignor to Phillips Petroleum Company, a corporation of Delaware Filed May 29, 1958, Ser. No. 738,807

6 Claims. (Cl. 250-435) This invention relates to the underground storage of fluids, such as gaseous ethylene, propane, butane, ammonia, etc., and liquids such as liquefied petroleum gas. In another aspect it relates to a method and apparatus for accurately locating the interface in an underground storage cavern or the like between two immiscible fluids having different densities, such as the interface formed between a pool of brine and a layer of liquefied petroleum gas stored thereabove in said cavern.

Constantly expanding production of fluids for the industn'es of this country and elsewhere has created a definite problem in providing suitable storage facilities for these fluids. In the petroleum industries, in particular, the problem of storage of gases such as ethylene, propane, butane, ammonia, etc., and liquids such as liquefied petroleum gas (hereinafter termed LPG), is

presently an urgent one due to the cost of storage in sur-' face equipment, such as steel tanks, and due to the massive construction required to withstand the vapor pressure of such stored fluids. Also adding to this problem of adequate storage facilities is the fact that many industn'es, particularly the LPG industry, experience seasonal peak loads in the requirements of their products and corresponding seasonal slack periods. These fluctuations in requirements require large storage facilities and the advantages of storing such fluids in underground storage caverns have lately come to the attention of the industry.

These underground storage caverns are generally formed in impermeable earth formations either by conventional mining methods or, in some cases, by dissolving out material with aqueous solvents or the like to create a storage space in soluble underground formations, for example, in salt formations and domes. The resulting caverns are less expensive to provide than would be an equal volume of orthodox surface storage space and have proven their value in the storage of gases, such as ethylene, propane, butane, ammonia, etc., and liquids such as LPG, and the like. After formation of the cavern, a pool of brine or other displacing liquid normally occupies the lower portion of the cavern and the product to be stored occupies the space in the upper portion of the cavern above the displacing fluid. Since the displacing fluid and stored product are generally immiscible and have different densities, an interface forms between these two fluids.

It is often necessary to know the location and keep trace of the interface between the, displacing fluid and the stored product in the cavern. For example, in order to determine the shape and size of a cavern, the amount of product stored in the cavern, etc., it is necessary to first locate the interface in order to make these determinations. Moreover, it is often necessary to know the location of the interface so as to be able to maintain the level of fluids in the cavern and thereby prevent collapse of the cavern roof, damage to the casing foot, and to pre vent stored product from passing up through the bottom of the wash pipe or eductor tubing which depends with- 2,972,050 Patented Feb. 14, 1961 in the cavern. Because the cavern is located a substantial depth below the ground surface, the caverns access bore is relatively small, and the shape of the cavern is often irregular, many of the prior art methods of locating the interface level or depth have been found wanting.

Accordingly, an object of this invention is to accurately locate the interface in an underground storage cavern or the like between two immiscible fluids having different densities. Another object is to provide a method and apparatus for locating said interface in spite of the relative inaccessibility of the cavern, the relatively small cavern access bore, and the irregular shape of the cavern. Another object is to provide apparatus which will indicate at the surface the location of said interface with accuracy and without requiring costly equipment. A further object is to provide a method and apparatus which will locate said interface in an easy, inexpensive manner and thereby make it possible to maintain accurate control over the level of fluids in the cavern. Other objects and advantages of this invention will become apparent from the following discussion, appended claims and drawing in which:

Figure l is a schematic elevational view in partial sec-v tion of an underground storage cavern and associated means necessary to practice the subject invention;

Figure 2 is a view similar to Figure 1 illustrating a modification thereof; Figures 3, 3A are views of buoyant means which serv as a source of radioactivity; and,

Figures 4, 4A and 5, 5A are views similar to Figures 3, 3A illustrating further embodiments thereof.

Referring now to the drawing, in which like parts have been designated by like reference numerals, and initially to Figure 1, an underground storage cavern generally designated 10 is shown. Cavern 10 is located or formed within a soluble underground formation 11, such as a salt formation. This cavern generally will have an irregular shape, such as that shown in the drawing, due to the fact that formation 11 may have some relatively insoluble materials embedded therein, such as anhydrite or gypsum, or may contain relatively insoluble shale stringers, or its irregular shape may be due to variations in mining or washing operations. However, the cavern may have a regular shape, such as that of an upright or inverted cone, or can be somewhat cylindrical in shape. Underground storage caverns of thesetypes can be formed by methods well known in the art, such as that disclosed in U.S. Patent 2,787,455, issued April 2, 1957, to R. S. Knappen. Generally, solution mined caverns are formed by drilling an access bore or bore hole 12 from the surface of the ground through relatively insoluble overlying formations 13, such as surface soil, shale, limestone, sandstone, etc., into the top of a soluble salt formation 11 and therebelow. Casing 14 is inserted in bore hole 12 and set or maintained therein' by cement 16 so as to form a fluid-tight seal, the lower end of casing 14 preferably depending below the top from salt formation 11. A tubing 17 is then lowered within casing 14 in annularly spaced relationtherewith, the botom of tubing 17 depending below the bottom of casing 14. The upper end of casing 14 is provided with a suitable surface conduit 18 having a valve 19' and pressure gauge 21 affixed thereto, conduit 18 communicating with the annulus 22formed betwen casing 14 and tubing 17. The upper end of tubing 17 extends upwardly through the closed upper end of casing 14 and communicates with a suitable surface conduit 23 provided with a valve 24 and pressure gauge 26, the upper end of tubing 17 being also provided with a valve 27. Alternatively, another tubing (not shown) ,can be-inserted' 17 during the washing operation. The salt in formation 11 is dissolved by circulating a solvent, such as fresh water, through the top of tubing 17 and out the bottom thereof, the resulting solution, such as brine, formed by the action of the solvent on the formation being displaced and removed to the surface via annulus 22 and conduit 18. As the solution of the formation llcontinues, tubing 17 can be incrementally lowered deeper into the formation, and occasionally raised to facilitate washing. Alternatively, the access bore can be initially drilled to an ultimate depth at which the bottom of the proposed cavern will be and the lower end of the tubing placed adjacent thereto and maintained there during the washing operation. In some cases it is advisable to inject a layer of hydrocarbon material, such as LPG, into the progressively enlarged cavern in such a manner that it floats on top of the pool of brine or wash solution 28 and thereby prevents the wash solution from contacting the roof of the cavern so as to prevent its collapse, or to prevent the wash solution from destroying the seal formed above the casing foot, thereby preventing subsequent leaks in the access bore. The protective blanket can be any material which is lighter than and immiscible with the wash solution 28, and can be the same as the subsequently stored product. During formation of the cavern, the circulation can be reversed as desired, that is, wash liquid can be introduced via conduit 18 and annulus 22, and resulting solution or brine removed from the cavern via the inner tube 17. After the cavern has been formed, product 29 is introduced therein, for example, via conduit 18 and annulus 22, the brine or wash solution 28 being displaced from the cavern via tubing 17, and an interface 39 being formed between the product and brine. When it is desired to remove some or all of the product 29 from the cavern, brine or other wash solution is introduced back into the cavern via tubing 17, thereby displacing product 29 via annulus 22 and conduit 18.

As mentioned hereinbefore, it is often necessary to locate and keep track of the interface 30 formed between the wash or brine solution 28 and the stored product 29.

According to one embodiment of this invention, one or more buoyant containers 31, containing a small amount of radioactive material, is placed in the cavern, for example, by dropping the container through the upper end of tubing 17 and pumping it down therethrough, preferably with fresh water, at a sufiicient velocity so as to cause the buoyant means 31 to be released from the bottom of tubing 17, whereupon it immediately rises along with the fresh water and floats on the top of brine 28 or at the interface 30 formed between the brine and product 29. The buoyant means or float 31 contains a source of penetrating radiation and the intensity of this radiation will be greatest at the point of interface 30, the detectable emission lasting for a suitable time, e.g., 30

days. Subsequent to the placement of buoyant means 31 in the cavern, a radiation detector 32, such as a Geiger counter, is lowered within tubing 17 by means of an armored cable 33. Cable 33 extendsupwardly through tubing 17 to the surface and passes through valve 27 and stufiing box 35, over a depth measuring sheave 34 at the surface of the earth to a cable reel 36 by means of which the cable in the tubing 17 may be lowered or raised. Electrical contact between the electrical conductor of the cable 33 and electrical apparatus at the surface of the earth can be made through the slip ring and vbrush connection 37 on the cable reel 36. The surface equipment preferably comprises an amplifier 38 and a recorder 39,

the surface apparatus being grounded at point 40 on the p scope of this invention to include one or both of these elements in the radioactivity detector 32 within tubing 17. The detector 32 is moved vertically through tubing tensity of its response to the radiation emitted from the buoyant means 31 will be greatest, that is, when the detector shows a maximum response it will be known that the detector is at that instant horizontally opposite the buoyant means 31. The response of detector 32 is continuously amplified and recorded by the surface equipment and a record of the detector output is correlated with the depth of the detector in tubing 17 as measured by the cable measuring device or sheave 34. Thus, by passing the detector 32 through the tubing 17 an accurate measurement is made of the depth of the interface 30.

Referring now to Figure 2, depending within casing 14,

' which is somewhat larger than the corresponding casing of Figure l, in addition to tubing 17 is a second tubing 41, the lower end of which is located substantially below the interface 30. vThe interior of tubing 41 is in communication with the annulus 22 by reason of a communieating valve conduit 42 at the well head. Because of this communication, the interface within tubing 41 will be at the same depth as that interface outside tubing 41. The upper end of tubing 41 is preferably provided with valves 43 and 44. When it is desired to measure or locate the interface 30, the buoyant means 31 is inserted in the upper end of tubing 41 with valves 43 and 44 opened and then closed in sequence to prevent escape of product, and the buoyant means is allowed to drop through the tubing 41, whereupon it floats at the interface therewithin. After placement of the buoyant means 31 at the interface within tubing 41, the radiation detector 32 is then lowered through tubing 17 in the manner described hereinbefore in regard to Figure 1, and the interface depth recorded as before.

Referring now to Figures 3, 3A, one embodiment of the buoyant means of this invention is illustrated. In these views, the buoyant means 51 comprises two discs i 52, 53 which are secured together, for example, by means cork or the like, the buoyant means having a density, for

example, of 0.75. By selecting bolts or other means of proper weight the buoyancy of the means 51 canbe adusted so that it will be lighter than the brine and heavier A than the stored product.

In Figures 4, 4A, a further embodiment of the buoyant means of this invention is shown and generally designated 58. In this embodiment, two hemispheres of buoyant material 59, 61 are screwed or otherwise fastened together, there being a sealed hollow portion 62 there- 'within, the relative weight of the hemispheres and size Indiana; this material is made from a powdered mixture magnetic material.

of the hollow being such as to insure the proper buoyancy. Embedded in an orderly or irregular fashion in the hemispheres 59, 61 are a plurality of permanent magnets 63.

Alternatively, the hemispheres 59, 61 can be made of. A particularly useful material which can be used to make the buoyant means magnetic is barium ferrite (BaFe O which is sold at Indox I, a product of Indiana Steel Products Company, Valparaiso,

the steel tubing 17. .In this manner, the:chances that the buoyant means will float. at a distance somewhat re-- mote from the tubing 17 are lessened. Buoyantmeans 58 is also provided with a source of radioactivity, for

, example, in a capsule64 attached to, the inner end of a bolt 66 which passes throughoneof the hemispheres 59,

61, the capsule preferably being centrally located within hollow 62.

Referring now to Figures 5, 5A, another embodiment of the buoyant means of this invention is shown and generally designated 71. The latter comprises two hemispheres 72, 73 having suitable flanges which are secured together, for example, by means of bolts 74 and nuts 76, anddefining hollow 77, the weight of the hemispheres and bolts and the size of the hollow being such as to insure the proper buoyancy. The hollow 77 formed with in hemispheres 72, 73 contains a source of radioactivity,

for example, a capsule 78 centrally positioned within hollow 77 by reason of a peg or. other supporting means 79. Alternatively, the hemispheres can be previously subjected to irradiation so as to emit detectable radioactivity itself.

The radioactive material contained within any of the aforementioned buoyant means can be any radioactive material, preferably an isotope such as 8 to 10 millicuries of iodine 131, which will emit detectable radioactivity, such as gamma rays, neutron rays, and beta rays. Preferably, the radioactive isotope is one which will emit gamma energy and will have a sufliciently long half-life. Suitable gamma ray emitters representatively include lanthanum 140 (40 hours half-life), antimony 124 (60 days half-life), iron 59 (35.5 hours half-life), tantalum 182 (117 days half-life), zirconium 95 (65 days half-life), and the like.

A number of instruments are known in the art which can be employed to detect such radiation. Probably the most common of these instruments is the Geiger counter which comprises a cylindrical cathode having an elongated anode therein. The two elements are contained within an envelope which is filled with a gas at a relatively low pressure, and an electrical potential is applied across the anode and cathode through an impedance element. This potential is maintained at such a level that the counter will conduct electricity when the gas within the envelope is ionized by radiation entering the chamber. These counters usually are adapted to provide a single output pulse representative of each radiation unit impinging thereon.

A second form of measuring instrument is the proportional counter which comprises an ionization chamber containing two spaced electrodes having a relatively high electrical potential thereacross. The space between the electrodes being filled with an ionizable gas at a pressure considerably higher than in a Geiger counter so that a continuous current flows between the electrodes at all times. The magnitude of this current is a function of the degree of ionization of gas between the electrodes, and this in turn, is a function of the radiation impinging upon the counter. This type of counter thus provides an indication of the magnitude of the radiation being detected.

A third type of presently known counter makes use of the phenomenon that radioactive substances cause momentary light emission or scintillations when their emitted radiation impinges substances such as zinc sulfide. These scintillations can be measured by an electron photo-multiplier tube.

Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention, and it is to be understood that the foregoing discussion and appended drawing illustrate preferred embodiments of this invention and do not unduly limit the same.

I claim:

1. In combination with an underground storage cavern completely enclosed by an impermeable formation for storing large volumes of fluid products including an access bore from ground surface, a heavier liquid in a lower level and a lighter fluid in an upper level thereof immiscible with said heavier liquid and forming an interface therewith: a first tubing suspended through said bore from ground level to a level below said interface; a capsule containing a source of penetrative. radiation floating on said interface within said first tubing free to move therein; a second tubing suspended through said bore from ground level to a level below said interface spaced close to said first tubing; a radiation detector on a line within said second tubing and movable vertically thru the area of said interface; means for measuring the depth of said detector; and amplifying and recording means sensitive to said radiation for detecting the level of said source of radiation.

2. The combination of claim 1 wherein said capsule comprises two similar housing members made of buoyant material, and a small quantity of radioactive material disposed within said housing members.

3. The combination of claim 1 wherein said capsule comprises two similar buoyant disc members provided with a cavity therebetween, means securing said discs together, and a small quantity of radioactive material disposed within said cavity.

4. The combination of claim 1 wherein said capsule comprises two similar hemispheres defining a hollow therebetween and threadedly secured together, a plurality of permanent magnets embedded in said hemispheres, and a small capsule of radioactive material centrally suspended in said hollow.

5. The combination of claim 1 wherein said capsule comprises two similar hemispheres made of magnetized barium ferrite, said hemispheres defining a hollow therebetween, means securing said hemisphere together, and a small capsule of radioactive material centrally suspended in said hollow.

6. The combination of claim 1 wherein said capsule comprises two similar hemispheres defining a hollow therebetween, said hemispheres having complementary peripheral flanges, means securing said flanges together, and a small capsule of radioactive material centrally suspended in said hollow.

References Cited in the file of this patent UNITED STATES PATENTS 2,456,233 Wolf Dec. 14, 1948 2,588,210 Crisman Mar. 4, 1952 2,700,734 Egan et a1 Jan. 25, 1955 2,869,642 McKay et al J an. 20, 1959 

